In recent years, photovoltaic power generation has been attracting attention as a clean energy source from the viewpoint of global environment conservation. A solar battery has recently been mounted in a hybrid car (HV car) or an electric automobile (EV car). As a charging device of a solar battery for an electric automobile, for example, a charging device described in Patent Literature 1 is known. The charging device described in Patent Literature 1 includes a charger which enables charging of a solar battery and a battery through the contacts of a relay. In this case, when the output voltage from the solar battery reaches a given value, the contacts of the relay are opened to perform charging of the battery.